"Process sampling" (as it is often referred to) is widely used for analyzing characteristics of liquids present in particular flow lines of process equipment. For example, the manufacturer of a pharmaceutical compound may want to test a characteristic of such compound (or of an ingredient thereof) for purity or concentration.
As other examples, water is used in power generation and in the manufacture of electronic products. Those who are carrying out such processes often wish to measure the presence of, e.g., silica, sodium and/or dissolved oxygen in the water or measure water turbidity.
For most applications, process sampling is carried out while the process is ongoing and while fluid is actually moving in the fluid flow line. And it is often desirable to draw samples of a particular fluid from several different locations in the process equipment. A common way of doing so is to mount a sampling nozzle at each such location (and such locations may be quite far apart from one another) and pipe fluid from the nozzles to a centralized sampling and analysis location where the sampling valves are located. Such valves are operated in some sort of coherent sequence.
The fluid samples drawn from such sampling valves are directed to a fluid analyzer. Such an analyzer is a device configured to provide information about one or more sample parameters, e.g., pH or dissolved oxygen content. Because fluid analyzers are relatively expensive, the practice is to use a single analyzer to provide information about fluid taken from each of several different locations in process equipment. Since samples are taken from any particular location at periodic intervals (rather than continuously), samples are taken from several locations in sequence and are routed to the analyzer in the same sequence.
A control device is often used to operate the several sampling valves. Such device, a programmable logic controller, a timer relay, a computer or the like, may be "programmed" to operate each of several sampling valves according to some coherent sampling strategy, often involving some sort of sequential valve operation.
While arrangements like those described above are generally satisfactory for their intended purpose, they tend to be characterized by certain disadvantages. One disadvantage is that mounting an individual sampling valve at each of several sampling locations is cumbersome and expensive in both labor and material. And if a single analyzer is used for several widely-spaced sampling valves, the volume of the "dead" fluid between a sampling valve outlet port and the analyzer may be very substantial. (Of course, the analyzer cannot be mounted adjacent to all of the separate, widely-spaced valves.) Dead fluid volume is an important concern and can have a direct bearing on the accuracy with which the analyzer provides information about the sample.
These factors suggest the use of a multi-port valve and, in fact, one type of multi-port fluid sampling valve is shown in technical literature titled "Whitey `T2` Series Valves" and bearing the name "Swagelok Co." However, configurations of the depicted valve appear to have certain deficiencies. One is that it relies upon one or more O-rings for sealing at critical locations such as between the inlet and outlet ports. And other O-rings are used as sliding seals. It is thought that O-rings can prove unreliable, particularly in the presence of fluid contaminants and/or when used as dynamic seals.
Another apparent deficiency is that the inlet and outlet ports and passages are arranged so that inlet pressure is in a direction tending to lift the O-ring sealing between the inlet and outlet ports. Sealing is solely by spring pressure which must be sufficiently high to overcome this "liftoff" tendency and assure a good seal.
The apparent need for high spring force probably accounts for the fact that the Whitey valves are pneumatically operated. It seems at least possible that spring pressure must be so high that a pneumatic actuator is required to operate the valve. Compressed air or other compressed gas is not often available at sampling locations or, if provided, is expensive to install. And, often, a device known as an "I-to-P" valve is needed and the current cost of such a valve is on the order of $100 each. (The I-to-P valve derives its name from the fact that it converts an electrical current signal, I, into a pressure signal, P.)
Other valves are shown in the patent literature. For example, U.S. Pat. No. 3,747,623 (Greenwood et al.) depicts a fluid flow control manifold with solenoid operated valves. Such manifold uses what are shown as looped tubes, one each for inlet and exhaust. Each valve has a pair of inlet ports connected together and a pair of outlet ports connected together. The solenoid controls two valves in tandem, one of which closes when the other opens.
That is to say, no valve is capable of operation by itself and no valve is capable of porting flow from a single inlet port to an outlet port. And the external tubing includes 90.degree. bends which may contribute to fluid "dead legs" and, at the least, contributes to pressure drop along the tubing. Thus, neither the valves nor the manifold are suitable for sampling from individual lines.
U.S. Pat. No. 5,259,416 (Kunz et al.) depicts individually operable valves, each sealing against a flat-faced truncated-cone-shaped valve seat. The Kunz et al. valve has a common inlet and separate outlets. Actuation of either valve directs flow from the common inlet to only one of the outlets. Fluid flows from both outlets only if both valves are actuated.
U.S. Pat. No. 4,611,631 (Kosugi et al.) involves a poppet-type changeover valve with three passages and a closure member movable to seal against one or the other of two seats. While the patent does not so state, it appears from the arrangement of the closure member and the seats that port 2c is the inlet and ports 2b and 2d are outlet ports. The valve closure member shifts between two positions, either of which connects the assumed inlet to one of the assumed outlet ports. There is no opportunity to simultaneously flow fluid to both outlet ports.
U.S. Pat. No. 3,357,232 (Lauer) shows an analyzing apparatus which uses three ball-type, pneumatically-shifted shuttle valves to control flow. The user selects from one of two sample streams by introducing inert gas into port 5 or port 9. Either of two outlet pipes (e.g., pipes 11', 12'), are selected by introducing inert gas into port 14. But irrespective of the outlet pipe selected, all of the sampled fluid flows to a common gas analyzer. The legs 16, 21 do not carry fluid simultaneously and like the external tubing depicted in the Greenwood et al. patent, such legs have 90.degree. bends.
An improved manifolded sampling valve which resolves some of the deficiencies of prior art valves would be an important advance in the art.